Aircraft pollution analysis	Interact with data while viewing them in different ways Use different color tables and cross sections to identify trends and patterns

Observers may consider the pollution produced by air traffic to be too insignificant to worry about, but for one factor. Emissions of nitrogen oxides close to the top of the troposphere are shown to have a “radiative forcing” effect on surface temperatures of about thirty times that of surface emissions. Suddenly the effect of those aircraft has significance.

In 1994 Dr. Lee was assigned the problem of examining the three-dimensional distribution of aircraft emissions in the atmosphere. These data came from a large collaborative European project, the ANCAT emissions inventory. "From the start of the project we realized we would be dealing with a large amount of data, including geographic information," said Dr. Lee, " so we knew we would need a software tool capable of reading multiple formats and of combining to a single image."

The completion of the ANCAT inventory was daunting. First, other partners of the group compiled the flight paths of every jet aircraft worldwide, including scheduled and charter flights and smaller private jets that fly the same airspace as commercial aircraft. Second, in order to establish the quantities of emissions along every flight path, data on climb and cruise emissions for each jet type were calculated. For example, an aircraft climbing out from its departure airport uses many times more fuel per km than one cruising at high altitude.

The German Research Institute for Air and Space Travel provided a simulated model for each aircraft type. "Much of the data we used were available, albeit in a rich variety of formats," commented Dr. Lee. "It simply required a huge amount of standardizing and combining. Data verification, however, can be more difficult." Finally, the data were passed on to AEA Technology in the form of a 3D coordinate detailing final fuel usage and calculated NO_x emissions.

The next task was relatively simple — to multiply the flight paths by the emissions models for each aircraft type. The result was twelve arrays of data — one for each 1,000 m above sea level. Each is based on a 2.80 x 2.80 grid (a total of 147,456 data points to cover the earth, up to 17 km in the atmosphere). "Other members of the group had modeled fuel usage and NO_x emissions; now we needed PV-WAVE to see the results," said Dr. Lee. "That's where the software came into its own."

The system can open and display any data set, given a few descriptors. With his first experiments, Dr. Lee could read each of the data files in turn and see the emissions at each level of the troposphere. The world map provided with the software allows the picture to be superimposed on a globe. By using PV-WAVE’s color tables, areas of differing emissions can be shown as a “heat map.”

Taking the analysis further, Dr. Lee developed a simple PV-WAVE routine to load all the data sets simultaneously and display them on the earth’s surface. Further routine calls allowed Dr. Lee to " slice through " a longitudinal cross section. "The results of this graphical analysis highlighted the imbalance of emissions in the Northern Hemisphere, for example," commented Dr. Lee.

The ability to interact with the data allowed Dr. Lee to pinpoint features in the data. “We found we had a few lines appearing at the highest level, close to the tropopause — the band between the troposphere and the stratosphere. Much of these emissions can be explained by Concorde flight paths — following ‘the great circle route’ to the USA and Rio de Janeiro. One of the great benefits of PV-WAVE is its flexibility,” concluded Dr. Lee. “I can use them to interact with the data, view it in different ways, try different color tables and cross sections through the information to identify trends and patterns. The end result is that we can visually analyze our data, pick up on the features and present them to environment researchers who will be working with our output.”

Dr. Lee’s research, sponsored by the Department of Transport, will be used by the UK Meteorological Office’s Hadley Centre for Climate Prediction and Research, among others, to model future climate changes as part of the UK’s input to the Intergovernmental Panel of Climate Change’s program. Dr. Lee can be contacted at AEA Technology, National Environmental Technology Centre, E5 Culham Laboratory, Oxfordshire OX143DB.